JP3414526B2 - Manufacturing method of hollow container - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow molded product having a novel internal structure, and more particularly to a hollow molded product having a high rigidity and a high resistance to environmental stress destruction, and having a good balance. It concerns a container. [0002] In general, polyolefin resins are not only excellent in processing characteristics, chemical resistance and weather resistance, but also inexpensive. In particular, polyethylene resins and polypropylene resins are excellent in processing characteristics and are various in quality. It is used for applications.
Particularly for detergent containers, polyethylene having a relatively high molecular weight is used because of its easy processing characteristics. However, when a surfactant such as a detergent is used as a content, cracks are often generated based on external stress and internal residual stress. Therefore, development of a resin having high resistance to environmental stress fracture has been desired. Further, from the standpoint of resource saving, a molded article having a small thickness is required, and for this purpose, a resin having high rigidity needs to be developed. In general, when the density of polyethylene is reduced, the resistance to environmental stress cracking increases, but the rigidity decreases. In this case, it is necessary to increase the wall thickness in order to increase the rigidity of the molded product, which is not preferable from the viewpoint of resource saving. Further, when the rigidity of the resin is increased, the resistance to environmental stress cracking decreases. In this case, it is necessary to increase the thickness of the molded product in order to increase the environmental stress crack resistance, which is not preferable. Normally,
It has been practiced to widen the molecular weight distribution by multi-stage polymerization of polyethylene or the like to balance the two. However, in this method, the balance between the environmental stress crack resistance of the molded article and the rigidity (buckling stress) of the molded article cannot be said to be sufficient. Under such circumstances, it has been desired to maintain rigidity and resistance to environmental stress cracking even when the thickness of the molded product is reduced. SUMMARY OF THE INVENTION [0004] Under such circumstances, an object of the present invention is to provide a higher resistance to environmental stress rupture than a molded article made of a conventional polyethylene resin for blow molding. It is an object of the present invention to provide a molded product having a balance between stiffness and rigidity, that is, a hollow container having high stiffness, a small thickness, and high environmental stress fracture resistance. As a result of intensive studies to solve the above-mentioned problems, even when polyethylene having a melt index and density used for ordinary hollow molding is used, the polyethylene and polypropylene are used. However, if a specific viscosity ratio of a sialate close to the sialate involved in the molding is used, if each granular material is mixed at a specific ratio and directly molded by a hollow molding machine without going through the melt mixing step, a layered product will be formed inside the product. It has been found that a molded article having excellent resistance to environmental stress rupture can be obtained while maintaining or increasing the rigidity. That is, the problem is that the density is 0.930 g / cm ³ or more and 0.965 or more.
g / cm ³ or less and a melt index of 0.03
In a method for producing a hollow molded container using polyethylene having a g / 10 minutes or more and 5 g / 10 minutes or less, 40 to 5% by weight of the polyethylene is melted with respect to the melt viscosity η _pe of the polyethylene at a shear rate of 100 sec ^-1 . Substitute with polypropylene having a melt viscosity η _pp whose viscosity ratio η _pp / η _pe satisfies 0.3 <η _pp / η _pe <3, and directly blow-mold the respective granules without prior melt-mixing The method can be solved by a method for producing a hollow molded container characterized by being subjected to the following. Next, the present invention will be described in detail. (Polyethylene and polypropylene) The polyethylene constituting the hollow molded container according to the present invention is a polyethylene generally used for hollow molding in a field requiring environmental stress crack resistance such as a detergent container, and more specifically, a melt at 190 ° C. Index 0.03g /
10 minutes or more and 5 g / 10 minutes or less, with a density of 0.930 g / cm ³
A polyethylene of 0.965 g / cm ³ or less, in this case, a polyethylene homopolymer and a carbon number of 4
A copolymer of the above-mentioned α-olefin and ethylene may be used, but a copolymer of an α-olefin having 5 or more carbon atoms and ethylene is particularly desirable for effectively exhibiting resistance to environmental stress fracture. [0007] In the present invention, the polypropylene used for the partial substitution of polyethylene includes a polypropylene homopolymer, a random copolymer of propylene and ethylene, or an α-olefin having 4 or more carbon atoms, or a block copolymer. Including. In the present invention, the resistance to environmental stress rupture and the rigidity of the hollow-molded container are as follows. When the thickness of the container is constant, a random copolymer of propylene and ethylene, or an α-olefin having 4 or more carbon atoms, or a block. If the modulus of elasticity of the copolymer is too low, the resulting hollow molded article will have excellent environmental stress resistance, but will have poor rigidity. Therefore, the copolymerization ratio of ethylene or α-olefin with propylene is preferably within 5 mol%. In the case of a block copolymer, the content of the block portion (rubber portion) is preferably within 30% by weight of the entire polypropylene in view of the balance between resistance to environmental stress fracture and rigidity of the obtained hollow molded product. From the standpoint of drop strength and impact resistance of the hollow molded container, if the rigidity of polypropylene is significantly higher than the rigidity of polyethylene, the drop strength and impact resistance will be reduced. It is desirably not more than 0.5 times. However, from the standpoint of maintaining rigidity, it is desirable that the rigidity of polypropylene be equal to or higher than the rigidity of polyethylene. Further, the ratio η _pp / η of the melt viscosity of polyethylene and polypropylene at a shear rate of 100 sec ^-1 .
It is necessary that _pe is 0.3 <η _pp / η _pe <3 in order to obtain a hollow molded container excellent in resistance to environmental stress fracture and excellent in rigidity even if the thickness is reduced. η _pp / η _pe is 0.3
If it is below, the environmental stress resistance is not improved as compared with the polyethylene molded article used. When η _pp / η _pe is 3 or more, the resistance to environmental stress rupture is not improved as compared with the polyethylene molded article used. Why the ratio of melt viscosity of polyethylene and polypropylene at a shear rate of 100 sec ^-1 η _pp / η _pe
Is not clear whether 0.3 <η _pp / η _pe <3, but only when this viscosity ratio is satisfied, the polypropylene is dispersed in a layered form inside the resin during actual hollow molding. It is presumed that the structure is maintained even in the final hollow container, and that the hollow container has a reinforcing effect on environmental stress crack resistance. On the other hand, when the viscosity ratio is other than that, the polypropylene does not disperse in a layered manner inside the hollow molded container, and has a spherical dispersion structure.
It is estimated that the environmental stress fracture resistance is not improved.
The melt viscosities η _pp and η _pe at a shear rate of 100 sec ⁻¹ described above were measured at 190 ° C. using a capillary viscometer, and the capillary length / capillary diameter = 33.
Refers to the value measured in. When the proportion of the polypropylene substituted for polyethylene in the polyethylene is 40% or more, the impact resistance of the molded product is remarkably deteriorated, but when it is severe, molding may not be performed. When the proportion of polypropylene is less than 5% by weight, the effect of improving rigidity is not remarkable, and the resistance to environmental stress cracking is hardly improved. "Molding method" In order to obtain the hollow molded container described in the present invention, the above-mentioned polyethylene and polypropylene granules (generally referred to as pellets).
Must be directly blow-molded without prior melt-mixing. On the other hand, if the granular material obtained by melt-mixing in advance is directly blow-molded in a hollow, the resistance to environmental stress fracture is not improved. There is no particular limitation on the hollow blow molding machine used in the main molding, but it is particularly preferred that the polypropylene has a structure in which a layered structure of polypropylene can be easily formed by shearing inside the molding machine. This can be easily achieved by using a molding machine having a screw that does not have a mixing part of a dalmage type more than necessary. There is no limitation on the molding temperature and speed, but it is necessary to set molding conditions so that the container after molding has a layered structure inside. It is necessary that the polyethylene granules and the polypropylene granules are previously mixed at a predetermined ratio. For this, a commonly used mixer for granules such as a tumbler is used. If the mixing of this portion is insufficient, the obtained hollow molded container may be non-uniform, leading to a significant decrease in mechanical properties. The method for producing polyethylene and polypropylene used in the present invention is not particularly limited.
Polyethylene is produced using a chromium-based catalyst, so-called Phillips catalyst or Ziegler catalyst. When a Ziegler catalyst is used, it is preferable to use multi-stage polymerization in terms of balance between molding characteristics and physical properties. In general, it is desirable to use a catalyst which gives a polymer having high stereoregularity and high activity from the viewpoint of improving rigidity and preventing resin deterioration. The polyethylene and polypropylene granules obtained as described above may optionally contain a heat stabilizer,
An antioxidant, a weather resistance stabilizer, an antistatic agent, a lubricant and the like may be blended. Further, a dye, a pigment or the like, or a masterbatch thereof may be introduced into the mixture of these granular materials, if necessary. EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. (Example 1) 1) Polyethylene-A A copolymer of ethylene and hexene was produced using a Phillips catalyst to obtain granules. The resulting polyethylene has a melt index of 0.3 g / 10 min and a density of 0.95 g.
/ Cc. Shear rate of 100 sec ^-1
At 14,000 poise. 2) Polypropylene-a Showaromer MK112 (block copolymer) granules manufactured by Showa Denko KK was used. 2 of this polypropylene
The melt index at 30 ° C. was 2 g / 10 min, and the viscosity at 190 ° C. at a shear rate of 100 sec ⁻¹ was 7000 poise. 3) Mixing of granules Polyethylene-A and polypropylene-a were mixed at a weight ratio of 80:20 using a tumbler for 10 minutes. 4) Hollow molding Hollow molding was performed using a 50 mmφ hollow molding machine, and a flat bottle having an inner volume of 400 cc and a bottle weight of 32 g was produced by this molding machine. 5) Environmental stress rupture resistance (ESCR) Ten bottles prepared by the above method were filled with 10% of a nonionic surfactant diluted with water at a predetermined concentration, and placed in an oven at 60 ° C. When the internal pressure was applied and the time required for 50% of the test bottles to break was measured, 60
It was time. 6) Rigidity Sampling the side of the bottle created by the method 4) and J
Molded according to IS K6760, JIS K72
The measurement was performed according to the method of Example No. 03. The stiffness measured by this method was 12000 kg / cm ² . (Comparative Example 1) For the purpose of comparison with Example 1, in Example 1, except that the granular material was mixed by using an extruder (50 mmφ) and then melted and mixed using an extruder (50 mmφ) in Example 1. The molding was evaluated in the same manner as in Example 1. The rigidity was 12000 kg / cm ² , which was the same as in Example 1, but the ESCR was 15 hours, which was one quarter of that of Example 1. Comparative Example 2 For comparison with Example 1, a block copolymer having a melt index of 8 g / 10 min at 230 ° C. and a viscosity of 3000 poise at a shear rate of 100 sec ⁻¹ was used as polypropylene-a. When the same molding and evaluation as in Example 1 were performed, the rigidity was 12,500 kg / cm ² and the ESCR was 12 hours. Example 2 As polypropylene-a, 2
A melt index at 30 ° C. of 0.7 g / 10 min,
The viscosity at a shear rate of 100 sec ^-1 is 14000.
The molding was evaluated in the same manner as in Example 1 except that poise polypropylene homopolymer was used.
0 kg / cm ² and ESCR were 60 hours. (Example 3) 2 as polypropylene-a
A melt index at 30 ° C. of 0.2 g / 10 min,
The viscosity at a shear rate of 100 sec ^-1 is 26000
The molding was evaluated in the same manner as in Example 1 except that poise polypropylene homopolymer was used.
0 kg / cm ² and the ESCR was 65 hours. (Comparative Example 3) The same polyethylene and polypropylene as in Example 2 were used, but the same molding and evaluation were conducted as in Example 1 except that a melt mixing step was provided. The rigidity was 12,500 kg / cm ² and the ESCR Became 15 hours. Comparative Example 4 Polypropylene-a having a melt index of 0.1 g / 10 min and a sialate of 100 s
The same molding evaluation as in Example 1 was performed except that a polypropylene homopolymer having a viscosity at ec ^-1 of 50,000 poise was used. The rigidity was 12,000 kg / cm ² ,
ESCR was 20 hours. (Comparative Example 5) When the molding was evaluated using only the polyethylene granules used in Example 1, the rigidity was 11500 kg / cm ² and the ESCR was 11 hours. [Table 1] The hollow-molded container according to the present invention satisfies the above-mentioned constitutional requirements. Therefore, when it is made to have the same thickness as a molded product made of a conventional polyethylene resin for blow molding, Both buckling strength and environmental stress resistance are improved.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-55-108433 (JP, A) JP-A-60-38448 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 49/00-49/80 C08J 5/00 CES F-term 4J002

Claims (1)

(57) [Claims] [Claim 1] The density is 0.930 g / cm ³ or more and 0.9.
65 g / cm ³ or less and a melt index of 0.
In a method for producing a hollow molded container using polyethylene having a length of not less than 03 g / 10 min and not more than 5 g / 10 min, 40 to 5% by weight of the polyethylene is subjected to a shear rate of 100 sec.
In ^-1 was replaced with polypropylene having a melt viscosity eta _pp the ratio eta _pp / eta _pe of melt viscosity versus melt viscosity eta _pe of the polyethylene satisfy _{0.3 <η pp / η pe <} 3, and each of the granular A method for producing a hollow molded container, wherein the material is directly subjected to blow molding without melt-mixing in advance.